Archive for April, 2009

These cells look like fairly typical bone cells. They appear to be connected to each other by thin branch-like projections and are embedded in a white matrix of fibres. At their centres are dark red spots that are probably their nuclei. But it’s not their appearance that singles out these extraordinary cells – it’s their source. You’re looking at the bone cells of a dinosaur.

They come from an animal called Brachylophosaurus, a duck-billed dinosaur that lived over 80 million years ago. By looking at one of its thigh bones, Mary Schweitzer from North Carolina State University has managed to recover not just bone cells, but possible blood vessels and collagen protein too. Their presence in the modern day is incredible. Time usually isn’t kind to such tissues, which decay and degrade long before harder structures like bones, teeth and armour are fossilised.

This is the second time that Schweitzer’s team have recovered ancient protein from dinosaur bones. Two years ago, they pulled off a similar trick with collagen protein from the bones of Tyrannosaurus rex. That discovery was a controversial one, and many scientists were justly sceptical. Last year, one group reinterpreted the so-calledsoft tissuesas nothingmore than bacterial biofilms, “cities” of bacteria not unlike the plaque on your teeth or slime on moist rocks.

Now, Schweitzer has returned with another volley in the debate, and one which considerably strengthens the case for preserved Cretaceous proteins. From the bone of Brachylophosaurus, she has uncovered tissues that bind to antibodies designed to target collagen and other proteins not found in bacteria, including haemoglobin and elastin. And her experiments were duplicated by independent researchers from five different laboratories. It seems that her Tyrannnosaurus discovery was far from a one-hit wonder.

Snowball, the sulphur-crested cockatoo, is an internet superstar. He’s known for his penchant for grooving to music, notably Everybody by the Backstreet Boys. As the music plays, Snowball bobs his head and taps his feet in perfect time with it. If it speeds up or slows down, his rhythm does too. He is one of two parrots that are leading a dance dance revolution, by showing that the human behaviour of moving in time to music (even really, really bad music) is one that’s shared by other animals.

People who’ve attended parties at scientific events may question the ability of humans to move to a beat, but it’s a fairly universal skill and one that many people thought was unique to our species. After all, domesticated animals like dogs and cats don’t do it, and they spend their time with humans and have been exposed to our music for thousands of years. Other animals may produce periodic sounds or perform complex dances, but sensing and moving in time to complex rhythms is a different matter.

Snowball and his feathered friend Alex (the late, famous African grey parrot) could change all of that. Aniruddh Patel from San Diego’s Neurosciences Institute found evidence of Snowball’s excellent rhythm under laboratory conditions. Before Alex’s recent death, Adena Schachner from Harvard University (working with Alex’s keeper, the renowned parrot psychologist Irene Pepperberg) found that he could also match Snowball’s bopping.

Both groups of researchers believe that the parrots’ dancing skills depend on a talent for “vocal learning” – the ability to mimic the sounds of other individuals. To do this, animals need to have excellent coordination between their sense of hearing and their motor functions. Indeed, after searching YouTube for videos of dancing animals, Schachner only found evidence of moving to beats (a talent known as “entrainment”) among 15 species that practice vocal learning – 14 parrots and the Asian elephant.

HIV is an elusive adversary. The virus is so good at fooling the immune system that the quest for an HIV vaccine, or even a countermeasure to resist infections, has spanned two fruitless decades. But maybe a defence has been lurking in our genomes all this time.

Nitya Venkataraman from the University of Central Florida has managed to reawaken a guardian gene that has been lying dormant in our genomes for 7 million years. These genes, known as retrocyclins, protect monkeys from HIV-like viruses. The hope is that by rousing them from their slumber, they could do the same for us. The technique is several safety tests and clinical trials away from actual use, but it’s promising nonetheless.

Retrocyclins are the only circular proteins in our bodies, and are formed from a ring of 18 amino acids. They belong to a group of proteins called defensins that, as their name suggests, defend the body against bacteria, viruses, fungi and other foreign invaders. There are three types: alpha-, beta- and theta-defensins. The last group is the one that retrocyclins belong to. They were the last to be discovered, and have only been found in the white blood cells of macaques, baboons and orang-utans.

In previous experiments, Venkataraman’s group, led by Alexander Cole, showed that retrocyclins were remarkably good at protecting cells from HIV infections. They are molecular bouncers that stop the virus from infiltrating a host cell. The trouble is that in humans, the genes that produce retrocyclins don’t work. Over the course of human evolution, these genes developed a mutation that forces the protein-producing machinery of our cells to stop early. The result is an abridged and useless retrocyclin.

But aside from this lone crippling mutation, the genes are intact and 90% identical to the monkey versions. Now, Venkataraman has awakened them. She found two ways to fix the fault in human white blood cells, one involving gene transfer and the other using a simple antibiotic. Either way, she restored the cells’ ability to manufacture the protective proteins. And the resurrected retrocyclins did their job well – they stopped HIV from infecting a variety of human immune cells.

The courtship rituals of the spider Harpactea sadistica start innocently enough, with a dance and a hug. The male spider taps the female gently with his front legs and embraces her. But from that point onwards, things for the female go rapidly downhill. The male bites her and she becomes passive, allowing him to manoeuvre her into position. Like all spiders, his genitals are found next to his head, on a pair of appendages called the pedipalps. But unusually, his penis ends in a needle-sharp tip called an embolus.

The embolus sits at the end of a loop called the conductor. The male hooks one of these loops around the opposite embolus to steady it. Then, by rotating the anchored needle, he drives the point straight through the female’s underside and ejaculates directly into her body cavity. On average, he does this six times, moving slowly downwards and alternating between his two penises. The entire cringeworthy sequence lasts about 15 minutes and throughout it, the male spider never penetrates the female’s actual genital opening.

The species was discovered in Israel last year by Milan Rezac from the Crop Rsearch Institute in the Czech Republic. He named it well. H.sadistica practices a style of sex that’s understandably known as “traumatic insemination“. It’s disturbingly common among insects and other invertebrates, and is most famously practiced by bedbugs. But this is the first time that the behaviour’s been seen among the chelicerates – the group of animals that includes spiders, scorpions and mites.

You can see it happening in the videos below. In the first, the male spider bites and incapacitates the female. In the second, he hooks the conductor of one pedipalp around the embolus of another and, with rotating motions, drives it into the female. These videos aren’t pretty – you’ve been warned.

The autism spectrum disorders (ASDs), including autism and its milder cousin Asperger syndrome, affect about 1 in 150 American children. There’s a lot of evidence that these conditions have a strong genetic basis. For example, identical twins who share the same DNA are much more likely to both develop similar autistic disorders than non-identical twins, who only share half their DNA.

But the hunt for mutations that predispose people to autism has been long and fraught. By looking at families with a history of ASDs, geneticists have catalogued hundreds of genetic variants that are linked to the conditions, each differing from the standard sequence by a single ‘letter’. But all of these are rare. Until now, no one has discovered a variant that affects the risk of autism and is common in the general population. And with autistic people being so different from one another, finding such mutations seemed increasingly unlikely. Some studies have come tantalisingly close, narrowing down the search to specific parts of certain chromosomes, but they’ve all stopped short of actually pinning down individual variants.

This week, American scientists from over a dozen institutes have overcome this final hurdle. By looking all over the genomes of over 10,000 people, the team narrowed their search further and further until they found not one but six common genetic variants tied to ASDs. This sextet probably affects the activity of genes that connect nerve cells together in the developing human brain.

For many animals, living with others has obvious benefits. Social animals can hunt in packs, gain safety in numbers or even learn from each other. In some cases, they can even solve problems more quickly as a group than as individuals. That’s even true for the humble house sparrow – Andras Liker and Veronika Bokony from the University of Pannonia, Hungary, found that groups of 6 sparrows are much faster at opening a tricky bird feeder than pairs of birds.

After ruling out several possible explanations, the duo put the speedy work of the bigger flock down to their greater odds of including boffin birds. Individual sparrows vary greatly in terms of their skills, experiences and personalities. Larger groups are more likely to include the sharpest bird brains, or several diverse individuals whose abilities complement each other.

Wild animals constantly encounter new, unfamiliar and challenging situations and the ability to adapt to them more quickly may give social species an edge over loners. The problem-solving advantages of groups have been demonstrated in humans. Three people, far from being a crowd, solve intellectual tasks faster than pairs or individuals, even if they were the smartest of the sample. There has been much less research on other animals, although scientists have certainly found that large groups of birds or fishes find food faster and more efficiently than smaller groups.

But Liker and Bokony’s sparrow experiments are the first to show that large animal groups outperform smaller ones at problem-solving tasks where they have to invent new techniques. House sparrows are a good choice for a study like this. They are very social birds that live in flocks of anywhere from a few individuals to a few hundred. They are opportunists that use their relatively large brains to find food in all sorts of new environments.

It is literally very difficult to mend a broken heart. Despite its importance, the heart is notoriously bad at regenerating itself after injury. If it is damaged – say, by a heart attack – it replaces the lost muscle with scar tissue rather than fresh cells. That weakens it and increases the chance of heart failure later on in life. No wonder that heart disease is the western world’s leading cause of death and illness.

If that picture seems bleak, two teams of scientists have some heartening news for you. The first has found that the heart does actually have the ability to renew its cells, albeit to a limited degree. And the second group has discovered a cocktail of proteins can nudge this process along, at least in mice.

Taking heart

The heart is made of an exclusive breed of cells called cardiomyocytes, whose synchronised contractions provide the heart with its beat. The cardiomyocytes develop from a more basic layer of cells called the mesoderm, which also gives rise to bones, cartilage and other tissues. Now, Jun Takeuchi and Benoit Bruneau from the Gladstone Institute of Cardiovascular Disease have found that a cocktail of three proteins – Gata4, Tbx5 and Baf60c – are enough to transform mesodermal cells into beating cardiomyocytes.

All three are needed for the job. Together, they managed to switch on the full gamut of genes needed to program the mesoderm of embryonic mice into heart cells. When they were added, Takeuchi and Bruneau found signs of various proteins that are associated with developing embryonic hearts, even in parts of the mesoderm that would normally not turn into heart muscle. These out-of-place cells developed very quickly too, for they started beating before the mice’s own heart cells did.

That’s a massive achievement and one that’s completely unprecedented for mammals. Other groups have tried to use protein combos to produce cardiomyocytes in other species, but with little success. In chicks, certain combinations switched on genes involved in heart development, but never went the whole way. In frogs or zebrafish, which have simpler hearts, two proteins were used to produce heart cells, but with just a one in ten success rate. Takeuchi and Bruneau managed to do the same in 9 out of 11 mouse embryos.

In the forests of Singapore lives a spider that must be an arachnophobe’s worst nightmare. Most species are solitary hunters subdue their prey with venomous fangs, sticky silken webs or a combination of the two. But Scytodes uses a third trick – it spits a sticky, venomous fluid from its fangs that both traps its victims and poisons them (see video of related species). And it does this in packs – after hatching, spiderlings spend their early lives on their home web and they spit at, bite and devour prey en masse.

There are actually about 200 species of spitting spiders belonging to the genus Scytodes, and the specific species I’m talking about here was previously classified as Scytodes pallida. But Laura Yap, a student from the National University of Singapore, believes that it may be a new species entirely. For the moment, she refers to it simply as “Scytodes sp“, and she has provided the first thorough description of its behaviour.

But Scytodes also has a tender side, with mothers caring for their spiderlings before and after hatching. By collecting colonies throughout Singapore, Yap found that the vast majority consisted of either single adults or a mother and her young brood. After laying her eggs in a silken case, the mother carries them around in two of her limbs until they hatch (see below). That process depends on her, for the babies can’t break out of the tough egg sac unless he makes a cut in it first. Once they’ve emerged, they stay with her for several weeks, and finally leave the web just before they mature.

Having your arm in a cast can be a real pain but immobilising your hand in plaster has consequences beyond itchiness, cramps and a growing collection of signatures. Silke Lissek from Bergmannsheil University found that just a few weeks in a cast can desensitise the trapped hand’s sense of touch, and lower neural activity in the part of the brain that receives signals from it. The uninjured hand, however, rises to the occasion and picks up the sensory slack by becoming more sensitive than before.

Lissek recruited 31 right-handed people, each of whom had one fractured arm encased in a cast, and compared them to 36 uninjured people. She measured the sensitivity of their fingertips by touching them with a pair of needles that were brought increasingly close together, and noting the distance at which the two needles felt like just one.

She found that the uninjured recruits had equally sensitive fingers on both hands, but for the cast-wearers, the fingers of the injured hand had become less receptive (no matter which arm was plastered). The threshold distance at which they perceived two needles rather than one was further than the same distance for the uninjured recruits. The healthy hand, however, became more sensitive and could tell the needles apart even if they were closer together than normal.

Seals and sea-lions gracefully careen through today’s oceans with the help of legs that have become wide, flat flippers. But it was not always this way. Seals evolved from carnivorous ancestors that walked on land with sturdy legs; only later did these evolve into the flippers that the family is known for. Now, a beautifully new fossil called Puijila illustrates just what such early steps in seal evolution looked like. With four legs and a long tail, it must have resembled a large otter but it was, in fact, a walking seal.

Natalia Rybczynski unearthed the new animal at Devon Island, Canada and worked out that it must have swam through the waters of the Arctic circle around 20-24 million years ago. She named it Puijila darwini after an Inuit word referring to a young seal, and some obscure biologist. The skeleton has been beautifully preserved, with over 65% of the animal intact, including its limbs and most of its skull.

Puijila is a massive boon for biologists trying to understand the evolution of pinnipeds, the group that includes seals, sea lions and walruses. It’s not itself a direct ancestor, having branched off the evolutionary path that led to modern pinnipeds. It did, however, retain many of the same features that a direct ancestor would have had. “Puijila is a transitional fossil,” Rybczynski explains. “It gives us a glimpse of what the earliest stages of pinniped evolution looked like, before pinnipeds had flippers. And it suggests that in the land-to-sea transition, pinnipeds went through a freshwater phase.”

This familiar group evolved from land-dwelling carnivores and their closest living relatives are the bears and the mustelids (otters, weasels, skunks and badgers). For other marine mammals like whales and dolphins, the fossil record has given us dramatic visuals for the gradual transformation from land-dweller to full-time swimmer. But for pinnipeds, that transition is much murkier because until now, the earliest known seal Enaliarctos already had a full set of true flippers. Puijila changes all of that.

In the Origin of the Species, the ever-prescient Darwin wrote, “A strictly terrestrial animal, by occasionally hunting for food in shallow water, then in streams or lakes, might at last be converted into an animal so thoroughly aquatic as to brave the open ocean”. This year, on the 150th anniversary of the book’s publication, the walking seal that bears his name pays a fitting tribute to Darwin’s insight.